Draftsmen, architects, engineers, and others often find a need in their work for multiple scales to measure or represent linear distances in various units or ratios or to translate from one set of dimensional units to another. This need has traditionally been met by the provision of linear scale instruments having a multiplicity of distance scales printed or embossed on their surfaces. Conventional scale instruments may include two, four, or six distances scales depending on the cross sectional shape of the instrument. Scale instruments for drafting machines generally provide only two scales. Often, a number of scale instruments are required to be on hand to accommodate the various types of distance units and scale ratios which may be encountered. The presence of such a number of instruments often clutters a drafting board, and inconveniences and inefficiencies are encountered in finding the right scale instrument and manipulating it to search for the particular scale needed.
Scale instrument arrangements are known which employ interchangeable scale strips. In one such instrument, one scale strip is placed in a use position while two others are placed in storage positions within the instrument. In another arrangement, scale strips may be selectively extended from the instrument body or retracted into a storage position. However, such structural approaches to providing multiple scales achieve little advantage over conventional one-piece scale instruments, such as triangular scales, in the scales which may be selected.
Electronic solutions have been attempted to provide more flexible distance measurement. In such attempts, a single row of electronic display elements is provided along the edge of an instrument. Numbers representing a distance are punched in on keys on the instrument. Circuitry interprets the numbers entered and activates the appropriate display elements to represent the end points of the desired distance. While some advantages may be realized from such an instrument, the requirement of entering several numerals would become tedious if a large number of distances needed to be entered. Additionally, such an instrument would be very difficult to use in measuring an existing distance.